The purpose of this project is to determine the nature, and specificity or plasticity of trophic nerve function in the peripheral nervous system. Present studies with muscle involved determining whether histocompatibility differences had any influence on the survival of muscle allografts (grafts between genetically different animals of the same species). The results demonstrated that muscle grafts were rejected within 30 days regardless of whether they bore both major and minor or only minor transplantation antigens. It was interesting, however, that when lymph node cells were used to include immunological tolerance (i.e., neonatal tolerance) to muscle transplantation antigens that only muscle grafts with minor antigens survived and became innervated. In other experiments it was observed that rat taste buds exhibited alkaline phosphatase (ALK Pase) activity whereas mouse buds lacked this enzyme. The tongue tissue rather than the nerve appears to regulate ALK Pase since buds induced in rat tongue grafts by mouse nerve fibers still showed ALK Pase activity.